#include<iostream>
#include<cmath>
using namespace std;
int main(){
  double x1,y1,x2,y2,x3,y3,p,a,b,c,s;
  cin>>x1>>y1>>x2>>y2>>x3>>y3;
  a=hypot(x1-x2,y1-y2);
  b=hypot(x1-x3,y1-y3);
  c=hypot(x3-x2,y3-y2);
  p=(a+b+c)/2;
  s=sqrt(p*(p-a)*(p-b)*(p-c));
  cout.precision(2);
  cout<<fixed;
  cout<<s;
}